analysis of the anti-charmed baryon state at h1

Karin Daum

Madison, April 27th , 2005 1

Analysis of the anti-charmed baryon state at H1

Karin Daum – Wuppertal

Outline:

• Observation of the D*p(3100) 1) resonance at

H1• Summary from searches for D*p(3100)• Model assumptions for the analysis• Acceptance corrected ratios (D*p(3100))/(D*)• Conclusions

13th International Workshop on Deep Inelastic Scattering Madison, April 27th – May 1st , 2005

on behalf of

1) Since the spin is unknown “D*p(3100)” rather than “c” will be used

Karin Daum

Observation of the D*p(3100) resonance @ H1A.Atkas et al., Phys. Lett. B588(2004)17. HERA-I, 75 pb-1

DIS: 1 GeV2 < Q2 < 100 GeV2 Photoproduction: Q2 < 1 GeV2

Background fluctuation probability4 x 10-8 (Poisson) 5.4 (Gauss)

Confirmed by independentphotoproduction sample

Preliminary @ ICHEP2004:R(D*p(3100)/D*) = 1.460.32 %

Bare rateuncorrected

Karin Daum

Results of D*p(3100) searches

H1 observation in ep cc X

Negative results for c from:

ALEPH e+e- Z0 ccFOCUS N cc XCDF pp cc XBELLE e+e- (4s) B0B0

ZEUS ep cc X

Different physics processes investigated (except ZEUS)

Detailed analysis of D*p(3100) from H1 needed

Karin Daum

Model assumptions for the analysis

Assumption:

c-quarks from the hard sub-processinteracts with QCD vacuum to createcharmed hadrons e.g. D*, c, D*p(3100)

(ordinary fragmentation process)

Technical procedure for correcting data:

Use RAPGAP 3.1Mimic D*p(3100) by appropriate modification of mass and decay modes of D1 and D2 No spin assignment done, i.e. isotropic decay * LO QCD

Basic production process*of charmed hadrons: BGF

pseudo-rapidity = - log(tan(/2))D*-inelasticity z =(P•pD*)/(P•q)

The model will be normalised to the total D*p(3100)/D* yield when comparing with data

Karin Daum

Acceptance corrected Rcor(D*p(3100)/D*)

Kinematic region: 1<Q2<100 GeV2 & 0.05<ye<0.7

Systematic errors include uncertainties due to: D*, D*p selection, veto for D1D2, background shape, dE/dx-measurement,Variation of D*p(3100) fragmentation and pseudo-rapidity

1. In the visible D* range as given in our publication:

Visible D*p range: Pt(D*p)>1.5 GeV, -1.5<(D*p)<1

Visible D* range: Pt(D*)>1.5 GeV, -1.5<(D*)<1, z(D*)>0.2 (applied to inclusive D* and to D*s from D*p(3100) decay)

Rcor(D*p(3100)/D*) = 1.59±0.33% %+0.33-0.45

95% Upper limit from ZEUS for DIS : <0.59 %in different phase space: Q2>1 GeV2 & ye<0.95

pt(D*)>1.35 GeV, |(D*p)|<1.6, pt(D*)/Et

>10>0.12

preliminary

Karin Daum

Acceptance corrected Rcor(D*p(3100)/D*)

Systematic errors include uncertainties due to: D*, D*p selection, veto for D1D2, background shape, dE/dx-measurement,Variation of D*p(3100) fragmentation and pseudo-rapidity

1. In the visible D* range as given in our publication:

Visible D*p range: Pt(D*p)>1.5 GeV, -1.5<(D*p)<1

Visible D* range: Pt(D*)>1.5 GeV, -1.5<(D*)<1, z(D*)>0.2 (applied to inclusive D* and to D*s from D*p(3100) decay)

Rcor(D*p(3100)/D*) = 1.59±0.33% %+0.33-0.45

preliminary

2. Extrapolated to the full D* phase space in D*p(3100) decay:

Visible D*p/D* range: Pt>1.5 GeV, -1.5<<1 (applied to D* for inclusive D* and to D*p for D*p(3100))

(D*p(3100))/(D*) = 2.48±0.52% %+0.85-0.64

Karin Daum

(D*p(3100))/(D*) vs. event kinematics

s calculated from D*/D*pin p-system:^

1xzzxm+xp

obs2cobs

Invariant mass s depends on:Pt* of D*, D*p in p-systeminelasticity z of D*, D*pfragmentation value xobs of D*, D*p (I’ll come to the fragmentation issue later)

Karin Daum

(D*p(3100))/(D*) vs. event kinematics

W,Q2: MC follows data s: MC differs from data

s calculated from D*/D*pin p-system:^

1xzzxm+xp

obs2cobs

Statistical errors only

Karin Daum

(D*p(3100))/(D*) for D* observables

Compared to normal D* productionD* from D*p(3100) are:

Suppressed for central in the lab.Significantly softer in pt(D*) and z(D*)Closer to photon direction in p

The simple MC approach does not describe the data

Lab. frame

p-frame

zD*-cut replacedby xobs(D*p)-cut

Karin Daum

(D*p(3100)) for D*p observables

D*p(3100) production is:

Suppressed for central in the lab.Close to photon direction in p (These features are not described by the simple MC approach)

MC approach in reasonable agreement with pt- and z-distributions of D*p(3100)

Lab. frame

p-frame

zD*-cut replacedby xobs(D*p)-cut

Karin Daum

zD*-cut replaced by xobs(D*p)-cut

Fragmentation function of D*p(3100), D*

(E-pz)lab(D*p,D*)

(E-pz)lab

xobs(D*p,D*) =

Hemisphere

Analysis1 performed in p:

Project all particles in the hemisphere into plane perpendicular to directionDivide event into 2 hemispheres defined by the D* directionSum up all particles in D* hemisphere c-quark (including QCD-effects)

D* from D*p(3100) gets very little energy from c-quark

D*p(3100) fragmentation is hard (as expected from its mass)

1)Similar to analysis of Zuzana Rurikova,HFWG, Session 2

Karin Daum

ConclusionsPreliminary results on acceptance corrected ratio D*p/D* in DIS in the visible D* region is

Rcor(D*p(3100)/D*) = 1.59±0.33% % D*s from D*p(3100) decay are significantly softer than normal D*s D*p(3100) production in central lab suppressed D*p(3100) produced close to the photon direction D*p(3100) fragmentation is hard

The simple fragmentation approach with isotropic decaydoes describe W and Q2 of D*p(3100) productiondoes not describe D* properties from D*p(3100) decaydoes reasonably well for properties of D*p(3100), except for lab and *

+0.33-0.45

Karin Daum

Backup slidesPhysics related slides

Karin Daum

Remarks on D*p search by ZEUS

We observe:D* from D*p(3100) decay take only little energy of the eventProduction of D*p(3100)is different in from inclusive D* productionThe charged and neutral multiplicity in D*p(3100) events tends to be higher than in ordinary D* events

The ZEUS cut pt(D*)/Et>10 for background suppressionis designed just to remove high multiplicity events with little energy for the D*Furthermore: The kinematic & visible D* regions are not directly comparable

Karin Daum

D*signal form PL B599(2004)1

D*signals vs. XE from EPJ C16(2000)597

Limit(cD*p)/(D*)<0.3%

Distributions suggest thatD*’s with large XE are favoured

Furthermore:Decay length cut used in PL B599is a veto for small XE according toEPJ C16.

Remarks on D*p search by ALEPH

Karin Daum

D* @ LEP are producedpredominantly by beauty

Rb 22%, Rc 17%

<xE>cc 0.488

Similar shapes

Karin Daum

ALEPH, EPJ C16(2000)597

ALEPH Limit:

(cD*p)/(D*)<0.3%Likely to be NOT in disagreement

D*’s from charmAt LEP D* fragmentation functionsignificant softer than at HERAdue to QCD evolution

D*’s from c should lead to a shiftin XE by about –0.3

For xobs(D*)>0.7:(cD*p)/(D*)=0.17±0.13%

Karin Daum

Remarks on D*p search by Belle

Exclusive channel in B0 decay:

B(B0 cp)B(c D*p)/ B(c D*pp)<11% @ 90% C.L.

They indirectly conclude from their limit on

B(B0 cp)B(c D-p)/ B(c D-pp)<1.2% @ 90% C.L.

by arguing the c decay into pseudoscalar plus proton should be favoured that they are not in agreement with H1

BUT: it is not clear which decay mode is favoured, Depends on spin of the D*p(3100)

Not in contradiction with H1 result

Karin Daum

Remarks on D*p search by CDF

Charm production via gluon gluon fusionSimilar to BGF at HERA

CDF charm trigger sensitive to central rapidity in c.m.s.||<0.7 with 2 svtx tracks with pt>2 GeV

H1 sees:Soft D*s from D*p(3100) not central in c.m.s.

Karin Daum

Fixed target experiment180 GeV photons on 9Behadronic mass W~18 GeV

Hera: 60<W<280 GeV

nucleon

c threshold

Large phase space suppressionfor c in FOCUSNo Monte Carlo used by FOCUS

Remarks on D*p search by FOCUS

Karin Daum

D* fragmentation

Here D*p(3100)Is contributing

Karin Daum

Backup slidesAnalysis related slides

Karin Daum

All events scanned:

No anomalies observede.g. split tracks, wrongreconstructionSignal not due to kinematic reflections

HERA-II

Typical D*p candidates

HERA-I

Karin Daum

Systematic error for (c)/(D*) in visible D* region

Relative systematic errors:dm window 1.5 MeV instead of 2.5 MeV - 9 %Fit with our background model instead of (M(D*p)-M(D*)) - 12 %z(D*)>0.1 instead of z(D*)>0.2 - 21 %Exclude D1,D2 signal region by |m(D*)-2.45|>50 MeV + 18 %Uncertainty in dE/dx ± 10 %Re-weighting of c fragmentation function - 5 %Re-weighting of (c) distribution - 3 %

Total - 28 + 21 %

Total systematic error : -0.45+0.33%

Karin Daum

Systematic error for (c)/(D*) for full D* region

Relative systematic errors:dm window 1.5 MeV instead of 2.5 MeV - 10 %Fit with our background model instead of (M(D*p)-M(D*)) - 14 %z(D*)>0.1 instead of z(D*)>0.2 - 8 %Exclude D1,D2 signal region by |m(D*)-2.45|>50 MeV + 17 %Selection with xobs(c) instead of z(D*) - 15 %Uncertainty in dE/dx ± 10 %Re-weighting of c fragmentation function* + 28 %Re-weighting of (c) distribution - 4 %

Total - 26 + 34 %

Total systematic error : -0.64+0.85%

*If the xobs(c) cut is used instead of the z(D*) cut the systematic uncertainty due to fragmentation reduces to 11%

Karin Daum

Acceptance corrected c/D* yield ratio-III : shat

g system

ˆ1zzm+cp

But: we observe charmed hadrons instead of quarks

Normal procedure: Replace quantities of c-quark by those of D*

We measure also fragmentation variable xobs we can do better

pt2(D*)/xobs(D*)+mc

2 xobs(D*)

z(D*)(z(D*)/xobs(D*) - 1)s =

Karin Daum

Remarks on (cD*p)/ (D*)(xobs)

xobs(D*) very soft !

For xobs(D*)>0.5:

(cD*p)/(D*)=1.08±0.31%

For xobs(D*)>0.7:

(cD*p)/(D*)=0.17±0.13%

Karin Daum

Reconstruction of shat

log10(shatrec(pt))-log10(shatgen(pt))

=0.1hadronlevel

80.8 73.4 81.6%

64.8 67.1 93.2%

Bins in shat: 9-40-100-1000 GeV2

stability

Karin Daum

Systematics: dE/dx

Check of dE/dx selection efficiencies for protons using 0 in data and SPQ MC

SPQ MC

Agreement between data and MC ~±5%

pt and distributions for protons from 0 may be different for those from c use systematic error of ± 10%

Karin Daum

D* Signal

96-00 data 75 pb-1 DIS: Q²>1 GeV²

Good Signal/Background

3400 D*’s in DIS to start with

Golden channelD*+ D0

s (K)s

(low BR but clean signal)M(D*)-M(D0) = 145.4 MeV

D* signal regionsubsequently used

Mass difference technique:MD*=M(Ks) - M (K)

Non charm induced background“wrong charge D” : fake D0 (K++/ K--)+S

Karin Daum

Proton selection

Particle identificationvia dE/dx

- 3-5% accuracy- 8% MIP resolution

Most probable dE/dx

Use dE/dx for background suppression

Karin Daum

Background well described by D* MC and “wrong charge D” from data

Apply mass difference technique

M(D*p)=m(K p)-m(K)+MPDG(D*)

no enhancement in D* Monte Carlo

no enhancement in wrong charge D

• signal visible in different data taking periods

narrow resonance at M=3099 3(stat.) 5 (syst.) MeV

Opposite sign D*p mass distribution

Karin Daum

Signal in both D*-p and in D*+p

M(D*p) = m(Kp)-m(K)+m(D*)

Signal of similar strength observed for both charge combinations at compatible

M(D*p)

M(D*p)=3.096 0.006 GeVM(D*p)=3.102 0.003 GeV

Events1.78.25 Events6.84.23

Karin Daum

Signal in like sign D*p combinations?

No significant peak in like sign D*p

Reasonably described by D* MC and wrong charge D from data

Karin Daum

Look at the correlationof M(D*) vs. M(D*p)

the (D*p) signal region is richer in D*

Does the resonance come from D*’s?

M(D*p) [GeV]

D*p signal region

(D*p) side bands

Side band scaled to the widthof the signal window in M(D*p)

Karin Daum

M(D*p) = m(Kp)-m(K)+m(D*)

1) Charge conjugate always implied

Use proton inthis region

M(D*p)=3.104 0.003 GeV

Is the D*-p1) signal due to protons?

920= .)( pL

Well identified protons

Karin Daum

Physics changes on-resonance ?

Single particle momentum spectraare steeply fallingThis feature is preserved in thecombinatorial background of invariant mass analyses

Harder spectrum for particles from decay due to mass release

Harder spectrum for particles from decay of charmed hadronsdue to hard charm fragmentation

For illustration

Karin Daum

Look at momentum distribution of proton candidates w/o dE/dx

No dE/dx cuts !

The momentum spectrum of the particlesin the signal region is harder than in the M(D*p) side bands

Fit slope with exp {-p(p)}

M(D*p) [GeV]

Signal region=1.270.09

D*p side bands=1.740.06

D*side band=1.860.13

Karin Daum

No dE/dx cuts !

The momentum spectrum of the particlesin the signal region is harder than in the M(D*p) side bands

At large p(p) (>2 GeV)Signal clearly visiblewithout dE/dx

Karin Daum

Kinematic tests

2 )( PPM

)22( **22

* XDXDXD ppEEmm

2-Body Decay

Mass M independent of decay angle * only for correct mass assignment

wrong mass assignment

correct mass assignment M(D*) [GeV]

M(D*p) [GeV]M(D*p) [GeV]

CPQ MC

Monte Carlo expectation

Band like structure visiblein the M(D*p)-M(D*x) planein data?

Karin Daum

Kinematic test: D*p vs. D*

Go to the D*p signal regionand look at D*

-mass hypothesis excluded from theshape and range of D* mass distribution !

Karin Daum

Significance estimatesignal+background fit:

mass: 3099 ± 3(stat) ± 5(syst.) MeVwidth: 12 ± 3 MeV (cons. with exp. Resolution)

Numbers of signal and bgr Nb=45.0 ± 2.8 (within ± 2 =± 24MeV) Ns=50.6 ±11.2 (1.46 ± 0.32 % of D* yield, uncorrected in acceptance)

For significance estimate:Fit background only hypothesis Nb=51.7 +- 2.7Events in signal region: 95

Background fluctuation probability (52 → 95) : 4 x 10-8 (Poisson) 5.4 (Gauss)

Karin Daum

Search for charmed PQ, c D*p, in ZEUS1995-2000 data, 127 pb-1

Selection of D*, p close to H1 cuts

DIS (Q2>1 GeV): 592090 D*’sp (Q2<1 GeV):11670140 D*’s

No signal seen in D*p

Limits on c/D* for DIS:

R(cD*p/D*)<0.51% @95% C.L.

Including some systematic uncertainties But selection different from H1Production mechanism of c same as for D*

Karin Daum

Details of fit

Charges M[MeV] s[MeV] NS

D*-p + D*+p 3099 ± 3 12 ± 3 50.6 ± 11.2D*-p 3102 ± 3 9 ± 3 25.8 ± 7.1D*+p 3096 ± 6 13 ± 6 23.4 ± 8.6

Karin Daum

D* signal in DIS and photoproduction

● DIS cleaner signal● photoproduction: supporting evidence

Karin Daum

Acceptance effects?

M(D*p) = m(Kp)-m(K)+MPDG

Smooth variation with M(D*p) Shape reflects opening of phase space

M(D*p) [GeV]

Good p efficiency

Proton efficiency“Pion survival probability”

Karin Daum

Reflections from decays to D* ?

0* → D*

D* cuts of D*pproton selection

D1 , D

2 window

loose D* cuts selection

D* cuts of D*p selection

Expect 3.5 decays (D1

0* → D*) in D*p signal

Karin Daum

Could signal be due to decay D0* → D0 ?

D0* → D0 → D0 e+e-

electrons from -conversion ● asymmetric in energy● misidentified as proton and s ?

No accumulation at small mee

in D*p signal region or elsewhere

V0 with onecommon trackwith D*p

Karin Daum

Lots of further kinematic test

• Reflections from a possible signal in D*K mass distribution: ruled out

• Possible contributions from D* D with -conversion: ruled out

• Possible contributions from D /D D K: ruled out• Possible peak structures in all possible mass correlations with

all possible mass hypotheses of the particles making the D* and the D*p system to search for real or fake resonances, e.g , , , K ,, f no enhancements found

• Possible peak structures in all possible mass correlations among the proton candidate the remaining charged particles of the event with all possible mass assignments to search for real or fake peaks,no enhancements found

0 ++ 0S

Karin Daum

Investigation of D*p and associated K0’s

1.Selection of D* DIS-events (dm<170MeV,r+w charge)with V0 candidates

At least on track in common

No obvious K0 signal

D*p signal region

No indication for a K0 signal

Karin Daum

Investigation of D*p and associated 0’s

For M(D*p) 3100 MeV:M(slowp) close to the 0 massdue to kinematics.

Was studied for publication using primary tracks Conclusion: No problem

Check with tracks from secondary vertices

D*p signal region Wrong charge

D* MC CPQ MC

Karin Daum

0 signal in rc/wc D* sampleNo DTNV in commom

Select D0 K-+ and c.c.Search for with 0 appropriateQuark content

All possible combinations

M(D0)-M(D0)<170 MeV

|M(D0)-M(D0)-.1454|<2.5 MeV

No cut in M(K-++p) applied

p-selection as for D*p paper

No 0 signal left in dm-window !

Karin Daum

p-selection as for D*p paper

Selection: |m(p)-m(0)|<9 MeV

All possible combinations

M(D0)-M(D0)<170 MeV

|M(D0)-M(D0)-.1454|<2.5 MeV

(0) = slow(D*)

Signal in M(D*p) NOT faked by 0’s !

Karin Daum

Hera kinematics in ep collisions

E = 27.6 GeVe E = 920 GeVp

√s ~ 300-318 GeV (energy c.m.)

DIS kinematics:

Photon virtualityQ2=-q2

Electron inelasticity y

Scaling variablex

Hadronic mass W

Scattered e detected: Q² > 1 GeV Electroproduction (DIS)Scattered e not detected: Q² ~ 0 GeV Photoproduction

Kinematic regimes

Karin Daum

Systematics: variation of c fragmentation function

xobs(c)

StandardRAPGAP

Most sensitive to xobs:z(D*)

2/NDF=1.52/NDF=2.82/NDF=3.9

Re-weighting offragmentation function

Karin Daum

New selection for D*p yield estimate: Xobs(c) > min (0.5 * P (proton), 0.5)

(use for acceptance corrected yields of c vs Zd , Xobs)

CPQ MC

Wrong charge D

Cut: xobs> min(0.5•p(p),0.5)

wrong charge D

CPQ MC

Cut in (D*p) fragmentation variable

Karin Daum

D*MC CPQ MC

Expected shift in peak position ~ -0.3

xobs(D*) very soft !

For xobs(D*)>0.5:

(cD*p)/(D*)=1.08±0.31%

For xobs(D*)>0.7:

(cD*p)/(D*)=0.17±0.13%

analysis of the anti-charmed baryon state at h1

q2 of d

properties of d

mimic d

normal d

inclusive d

eventproduction of d

ordinary d

total d

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